Among the various video display systems available in the art, an optical projection system is known to be capable of providing a high quality display in a large scale. In such an optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M x N, actuated mirrors such that each of the mirrors is coupled with each of the actuators. The actuators may be made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to an electric field applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture of a baffle. By applying an electrical signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from each of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as a projection lens, to thereby display an image thereon.
In FIG. 1, there is shown a cross sectional view of an array 10 of M x N thin film actuated mirrors 5 for use in an optical projection system, disclosed in a copending commonly owned application, U.S. Ser. No. 08/331,399, entitled "THIN FILM ACTUATED MIRROR ARRAY AND METHOD FOR THE MANUFACTURE THEREOF", comprising: an active matrix 11 including a substrate 12, an array of M x N transistors (not shown) and an array 13 of M x N connecting terminals 14; an array 15 of M x N thin film actuating structures 16, each of the actuating structures 16 having at least a thin film layer 17 of a motion-inducing material, a first electrode 18 and a second electrode 19, the first and the second electrodes 18, 19 being placed on top and bottom of the thin film motion-inducing layer 17, respectively; an array 20 of M x N supporting members 21, each of the supporting members 21 being used for cantilevering the corresponding actuating structure 16 in place, and also for electrically connecting the actuating structure 16 and the active matrix 11; and an array 22 of M x N mirrors 23 for reflecting light beams, each of the mirrors 23 being placed on top of the actuating structure 16. In the thin film actuated mirror array 10, an electrical signal is applied across the thin film layer 17 of the motion-inducing material located between the pair of electrodes 18, 19 in each of the actuating structures 16, causing a deformation thereof, which will in turn deform the mirror 23 placed on top thereof, thereby changing the optical path of the incident light beam.
One of the major problems associated with the above described array 10 of M x N thin film actuated mirrors 5 is the overall optical efficiency of the array 10. When each of the actuating structures 16 deforms in response to the electric signal applied across the thin film motion-inducing layer 17 thereof, each of the mirrors 23 attached thereto also deforms. However, in the array 10, the portion of the mirror 23 secured to the supporting member 21 does not deform in response to the electric signal, but remains securely in place, and furthermore, the portion of the mirror 23 that deforms bends to thereby create a curved top surface for reflecting the light beams. As a result, the overall optical efficiency of the array 10 decreases, as well as, by the effective length of the mirror 23 being reduced by the length of the portion of the actuating structure 16 secured to the supporting member 21, but also by the curved top surface of the mirror 23 when it bends.